Clusters and groups of galaxies in the 2dF galaxy redshift survey:: A new catalogue

We create a new catalogue of groups and clusters, applying the friends-of-friends method to the 2dF GRS final release. We investigate various selection effects due to the use of a magnitude limited sample. For this purpose we follow the changes in group sizes and mean galaxy number densities within groups when shifting nearby observed groups to larger distances. We study the distribution of sizes of dark matter haloes in N-body simulations and compare properties of these haloes and the 2dF groups. We show that at large distances from the observer luminous and intrinsically greater groups dominate, but in these groups only very bright members are seen, which form compact cores of the groups. These two effects almost cancel each other, so that the mean sizes and densities of groups do not change considerably with distance. Our final sample contains 10750 groups in the Northern part, and 14465 groups in the Southern part of the 2dF survey with membership N-gal >= 2. We estimate the total luminosities of our groups, correcting for group members fainter than the observational limit of the survey. The cluster catalogue is available at our web-site (http://www.aai.ee/similar to maret /2dfgr.html). (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.